(753b) Water-Soluble Drug Partitioning and Adsorption in Polyelectrolyte Hydrogels

Solute uptake and release in soft-contact-lens-material hydrogels is critical towards designing optimal care-packaging solutions for wetting and disinfection, mitigating lens fouling by lipids/proteins, and controlling ocular drug delivery. In these applications, the extent of solute uptake/partitioning is regulated by size, charge, and hydrophilicity of the aqueous solute and hydrogel matrix, and often, solute adsorption to the internal polymer strands [1,2]. This work reports experimental and theoretically predicted equilibrium water-soluble drug partition coefficients in hydrogels where specific adsorption on and electrostatic interaction with the polymer matrix are pronounced.

The hydrogels studied are representative of soft-contact-lens materials that have relatively high polymer content and are sometimes partially ionic. We employ two-photon confocal microscopy and back extraction with UV/Vis-absorption spectrophotometry.  Partition coefficients are obtained for ten prototypical small ionic and nonionic water-soluble drugs (e.g., acetazolamide, hydrocortisone, and sodium fluorescein) as functions of pH, hydrogel composition, and aqueous salinity. For the copolymer hydrogels studied, nonionic drug partition coefficients are significantly greater than the hydrogel water volume fraction indicating strong specific adsorption to the polymer chains. For all cases, drug partition coefficients are quantitatively predicted by accounting for hard-sphere size exclusion, Donnan electrostatic repulsion, and specific adsorption. All model parameters are obtained independently. Predicted partition coefficients are in excellent agreement with experiment. Importantly, the proposed model provides a framework for better design of SCL-material hydrogels to regulate equilibrium drug uptake and release.

[1] Dursch TJ, Taylor NO, Liu DE, Wu RY, Prausnitz JM, Radke CJ. Water-soluble drug partitioning and adsorption in HEMA/MAA hydrogels. Biomaterials 2014; 35:620-29.

[2] Kotsmar Cs, Sells T, Talyor NO, Liu DE, Prausnitz JM, Radke CJ. Aqueous solute partitioning and mesh size in HEMA/MAA hydrogels. Macromolecules 2012; 45:9177-87.